What a UUID is
A UUID (universally unique identifier, also called a GUID) is a 128-bit label written as 32 hex digits in groups, like 3f2b8c1e-5d4a-4f7b-9a21-0c6e8d1b7a43. Anyone can make one without asking a central authority, and the chance of two being the same is so small it can be ignored, which makes them handy as database keys, file names and tracking ids.
Version 4 or 7?
Version 4 is completely random apart from a few fixed bits that mark the version. It is the common choice. Version 7 starts with the current time in milliseconds, then random digits, so ids made later sort after ids made earlier. That keeps database indexes tidy and makes ids roughly sortable by creation time. The trade-off is that a v7 id reveals roughly when it was made.
Questions
Are they random enough? Yes. They use your browser’s secure random number generator, the same one used for passwords.
Are they stored or sent? No. They are made on your device and disappear when you leave; only your formatting choices are kept. For a password instead, see the Password Generator.
Can I remove the hyphens? Yes, turn off Hyphens for a plain 32-character string. Braces give the {...} style some Microsoft tools use.